System and method for ascertaining angle of arrival of an electromagnetic signal

ABSTRACT

A system for ascertaining angle of arrival of an electromagnetic signal having at least one signal characteristic indicating a first state or a second state includes: (a) a plurality of n antenna elements intersecting a common axis and cooperating to establish  2   n  sectors; each respective sector being defined by two antenna elements and the axis; the signal characteristic indicating the first state on a first side of each antenna element and indicating the second state on a second side of each antenna element; combinations of the signal characteristics in each respective sector uniquely identifying the respective sector; and (b) an evaluation apparatus coupled with the antenna elements and employing the state of the signal characteristic sensed by each of the antenna elements to effect ascertaining angle of arrival to a resolution of at least one respective sector.

This application claims benefit of prior filed Provisional PatentApplication Ser. No. 60/433,637, filed Dec. 16, 2002, and claims benefitof copending Provisional Patent Application Ser. No. 60/438,724, filedJan. 8, 2003.

BACKGROUND OF THE INVENTION

The present invention is directed to electromagnetic signal handling,and especially to direction finding using electromagnetic signals. Priorart techniques and apparatuses for radio direction finding have involveda pair of vertically oriented loop antennas with orthogonal axes and anomnidirectional antenna, such as a sense antenna. Such techniques andapparatuses employed amplitude comparison direction finding to ascertainthe angle of arrival of an electromagnetic signal.

A consequence of the requirement for several antennas and their relatedcomponents in implementing prior art radio direction finding techniquesis that the apparatuses for carrying out such prior art techniques arebulky. In the present market, smaller apparatuses are sought, so it isadvantageous to be able to accomplish required operations using morecompact apparatuses. Additionally, in the present market, it isadvantageous to have systems that are more reliable in intense multipathenvironments.

Furthermore, typical systems for positioning and locating a transmitteroften rely on range data gathered from a dispersed network of receivers.It is advantageous for a single receiving device to be able to locate atransmitter without relying on data from other receiving devices.

Similarly, existing receive systems employ “temporal rake” receiversthat combine signal components received at different times to optimizereception of a received signal. It is advantageous for a receive systemto be able to implement a “spatial rake” that selectively adds upsignals arriving from different angles.

Also, conventional omni-directional receive systems are vulnerable tointerfering signals arriving from particular directions. It isadvantageous for a receive system to have the ability to receive signalsomni-directionally yet decrease sensitivity to undesired or interferingsignals arriving from particular directions. Similarly conventionalomni-directional transmit systems may be prone to interfere withadjacent receivers lying in a particular direction. It is advantageousfor a transmit system to have the ability to transmit signalsomni-directionally yet decrease emissions in the particular direction ofan adjacent receiver.

Finally, typical systems for intrusion detection using broadband radarsystems rely on timing to yield a range gated detection perimeter. Anintrusion may be detected at a particular range, but an exact positionof an intruder is unknown. It is advantageous to have a system toidentify the angle of arrival of a radar signal to precisely locate anintruder or other reflecting object.

There is a need for a more compact and more reliable apparatus foreffecting radio direction finding operations to ascertain angle ofarrival of electromagnetic signals at an antenna.

SUMMARY OF THE INVENTION

A system for ascertaining angle of arrival of an electromagnetic signalhaving at least one signal characteristic (e.g., phase, polarization, oramplitude) indicating a first state or a second state (e.g., front orback) includes: (a) a plurality of n antenna elements intersecting acommon axis and cooperating to establish 2n sectors; each respectivesector being defined by two antenna elements and the axis; the signalcharacteristic indicating the first state on a first side of eachantenna element and indicating the second state on a second side of eachantenna element; combinations of the signal characteristics in eachrespective sector uniquely identifying the respective sector; and (b) anevaluation apparatus coupled with the antenna elements and employing thestate of the signal characteristic sensed by each of the antennaelements to effect ascertaining angle of arrival to a resolution of atleast one respective sector.

This invention exploits an attribute of antennas whose waveforms exhibita 180 degree phase shift (or an amplitude inversion) in signals receivedfrom opposite half-planes. This invention also exploits an attribute ofantennas which are sensitive to different polarizations in oppositehalf-planes. In fact, any antenna with a signal characteristic thatchanges in response to a first or second state (such as arrival from afront or back side) may be advantageously used by the present invention.

A method for ascertaining angle of arrival of an electromagnetic signalat an antenna structure; the method comprising the steps of: (1)configuring the antenna structure to include a plurality of n antennaelements intersecting a common axis and cooperating to establish 2nsectors; each respective sector of the 2n sectors being defined by twoantenna elements of the plurality of n antenna elements and the axis;(2) providing the electromagnetic signal with at least one signalcharacteristic; the at least one signal characteristic indicating afirst state on a first side of each respective antenna element of the nantenna elements and indicating a second state on a second side of eachrespective antenna element of the plurality of n antenna elements;combinations of signal characteristics in each respective sectoruniquely identifying the respective sector; and (3) evaluating the stateof signal characteristics sensed by each respective antenna element toeffect ascertaining angle of arrival to a resolution of at least onerespective sector.

It is, therefore, an object of the present invention to provide acompact apparatus for effecting radio direction finding operations toascertain angle of arrival of electromagnetic signals at an antenna. Inthe invention's most simplistic state, the system can dispense with anomni-directional sense antenna thus improving compactness.

It is a further object of the present invention to provide an improvedand more reliable system and method for ascertaining angle of arrival ofan electromagnetic signal.

A feature of the present invention enables a location aware receiverthat can locate a transmitter without a multi-lateration or othercalculation relying on data from a dispersed network of receivers.

An additional feature of the present invention enables a “spatial rake”receiver: a receive system able to selectively add up signals arrivingfrom different angles.

Another feature of the present invention provides a receive system withthe ability to receive signals omni-directionally yet decreasesensitivity to undesired or interfering signals arriving in particulardirections. Similarly a further feature of the present inventionprovides a transmit system with the ability to transmit signalsomni-directionally yet decrease emissions in the particular direction ofan adjacent receiver.

A still further feature of the present invention enables a system toidentify the angle of arrival of a radar signal to precisely locate anintruder or other reflecting object.

Further objects and features of the present invention will be apparentfrom the following specification and claims when considered inconnection with the accompanying drawings, in which like elements arelabeled using like reference numerals in the various figures,illustrating the preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a representative prior art antennaarray useful for radio direction finding operations.

FIG. 2 is a schematic diagram of electromagnetic signal patternsassociated with operating the orthogonal loop antennas illustrated inFIG. 1.

FIG. 3 is a schematic diagram illustrating patterns of waveforminversions related to quadrant of arrival of an electromagnetic signalat an orthogonal loop antenna of the type illustrated in FIG. 1.

FIG. 4 is a schematic diagram illustrating patterns of waveforminversions related to sector of arrival of an electromagnetic signal ata multi-element antenna apparatus.

FIG. 5 is a schematic diagram illustrating details of the preferredembodiment of an evaluation apparatus useful in the system of thepresent invention.

FIG. 6 is a schematic diagram illustrating details of a first alternateembodiment of an evaluation apparatus useful in the system of thepresent invention.

FIG. 7 is a schematic diagram illustrating details of a second alternateembodiment of an evaluation apparatus useful in the system of thepresent invention.

FIG. 8 illustrates a planar antenna for use with the present invention.

FIG. 9 illustrates a representative signal pattern of the antenna ofFIG. 8.

FIG. 10 illustrates a novel chiral polarization UWB slot antenna.

FIG. 11 illustrates a dual horn antenna system for use with the presentinvention.

FIG. 12 provides an isometric view of the dual horn antenna system ofFIG. 11.

FIG. 13 illustrates shows a transmitter and a receiver employedaccording to the teachings of the present invention.

FIG. 14 illustrates a typical transmitted signal and received signalssuch as may be received by an antenna system as taught by the presentinvention.

FIG. 15 is a flow chart illustrating the method of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The principle of reciprocity requires that reception and transmissionproperties of an antenna be reciprocal so that properties of an antennaare the same whether the antenna is employed for receiving signals or isemployed for transmitting signals. Throughout this description, itshould be kept in mind that discussions relating to transmitting ortransmissions apply with equal veracity to reception of electromagneticenergy or signals, and vice versa. In order to avoid prolixity, thepresent description will focus primarily on reception characteristics ofantennas, with the proviso that it is understood that transmission ofenergy or signals is also inherently described.

FIG. 1 is a schematic diagram of a representative prior art antennaarray useful for radio direction finding operations. In FIG. 1, a radiodirection finding antenna array 10 includes a first vertically orientedloop antenna element 12 arranged substantially perpendicular with afirst axis “y” and a second vertically oriented loop antenna element 14arranged substantially perpendicular with a second axis “x”. Axes x, yare typically orthogonal axes. Antenna elements 12, 14 intersect at avertical axis “z” that is perpendicular with axes x, y.

Each of loop antennas 12, 14 has a typical “doughnut” antenna patternwell known to experienced practitioners of the antenna arts. Such a“doughnut” pattern establishes minimal sensitivity to signals arrivingalong an axis perpendicular with the plane of the antenna element andmaximally sensitive along axes lying in the plane of the antennaelement. Such an antenna pattern has “front-back ambiguity”. Angle ofarrival of an electromagnetic signal at such a front-back ambiguousantenna element can only be determined with 180 degree accuracy. Toovercome such front-back ambiguity an omnidirectional antenna 16 istypically used with vertical loop antennas 12, 14 to unambiguouslyindicate whether a sensed signal (not shown in FIG. 1) arrives from the“front” or from the “back” of a respective antenna array.

FIG. 2 is a schematic diagram of electromagnetic signal patternsassociated with operating the orthogonal loop antennas illustrated inFIG. 1. In FIG. 2, antenna elements 12, 14 are shown in a top view withtheir associated axes x, y. Antenna pattern 22 is a planar section ofthe antenna pattern of antenna element 12. Antenna pattern 22 includesloops 19, 21. Antenna pattern 24 is a planar section of the antennapattern of antenna element 14. Antenna pattern 24 includes loops 23, 25.Planar antennas, such as planar loop antennas 12, 14, are maximallysensitive to signals in the plane of the loop, and minimally sensitiveto signals incident along the axis of the loop. That is, antenna element12 is minimally sensitive to signals arriving along axis y, and antennaelement 14 is minimally sensitive to signals arriving along axis x.Antenna patterns 22, 24 are mathematically expressed for two dimensionsin the x,y plane as:P(φ)=cos²φ  [1]where, φ=angle of arrival in the x,y plane.P(φ)=sin²φ  [2]where, φ=angle of arrival in the x,y plane.

Antenna patterns 22, 24 may be weightingly summed to create a virtualloop antenna pattern (not shown in FIG. 2) oriented in any direction inthe x,y plane. Such “steering” of the response patterns of antennaelements 12, 14 permits maximizing or minimizing a received signal toascertain its angle of arrival at antenna elements 12, 14.

Another prior art arrangement for ascertaining angle of arrival ofelectromagnetic signals at antenna elements 12, 14 is to effectamplitude comparison of signals received at antenna elements 12, 14 andemploying the relationship: $\begin{matrix}{\phi = {\tan^{- 1}\frac{A_{2}}{A_{1}}}} & \lbrack 3\rbrack\end{matrix}$

Expression [3] will only yield a magnitude for a value of angle ofarrival φ. That is, expression [3] can only produce a solution within a180 degree range; it describes antenna elements 12, 14 with “front-backambiguity”. It is for this reason that sense antenna 16 (FIG. 1) isemployed with radio direction finding antenna array 10 (FIG. 1). Anomnidirectional antenna 16 operates as a sense antenna to providedirectional input to the solution provided by expression [3], therebyresolving the front-back ambiguity suffered by antenna elements 12, 14.An omnidirectional antenna may be thought of as providing a sign for thesolution of expression [3] to enable determination of angle of arrivalof signals at antenna elements 12, 14 for a full 360 degree range.

A consequence of the requirement for both loop antennas 12, 14 and anomnidirectional antenna 16 for implementing prior art radio directionfinding techniques is that apparatuses such as radio direction findingantenna apparatus 10 are bulky. In the present market, smallerapparatuses are sought, so it is advantageous to be able to accomplishrequired operations using more compact apparatuses. There is a need fora compact apparatus for effecting radio direction finding operations toascertain angle of arrival of electromagnetic signals at an antenna.

The present invention provides significant improvements over prior artradio direction finding apparatuses and methods in ascertaining angle ofarrival of electromagnetic signals. The present invention employs acharacteristic electromagnetic signal. For purposes of this applicationa characteristic electromagnetic signal has at least one signalcharacteristic that experiences inversion or another detectable changewhen the signal is received by various portions of an antenna element.By way of example and not by way of limitation, a signal characteristicmay include phase, polarization, or amplitude. Also by way of exampleand not by way of limitation, a characteristic electromagnetic signalmay be a broadband electromagnetic signal having a characteristicGaussian doublet type waveform in the time domain. Such Gaussian doubletwaveforms are recognizable as having either an upright (or positive)orientation or an inverted (or negative) orientation. Further, suchGaussian doublet waveforms are known to exhibit 180 degree inversion insignals received or transmitted by a first half-plane of a planar loopantenna element compared with signals received or transmitted by asecond half-plane of a planar loop antenna. For purposes of thisapplication, the term “broadband signal” refers to a signal having asufficiently broad bandwidth to permit detection of a change in a signalcharacteristic of an electromagnetic signal interacting with (i.e.,received or transmitted by) an antenna element. For purposes of thisapplication, the term “broadband antenna” refers to an antenna signalhaving a sufficiently broad signal response to permit detection of achange in a signal characteristic of an electromagnetic signalinteracting with (i.e., received or transmitted by) the antenna element.

FIG. 3 is a schematic diagram illustrating patterns of waveforminversions related to quadrant of arrival of an electromagnetic signalat an orthogonal loop antenna of the type illustrated in FIG. 1. In FIG.3, antenna elements 12, 14 (FIG. 1) are shown in a top view with theirassociated axes x, y. A broadband electromagnetic signal containing aGaussian doublet is received by antenna elements 12, 14. Antennaelements 12, 14 establish sectors or quadrants I, II, III, IV. Forpurposes of succinctly describing operation of the apparatus illustratedin FIG. 3, antenna element 12 will be referred to as ANTENNA ELEMENT Aand antenna element 14 will be referred to as ANTENNA ELEMENT B.

FIG. 3 presumes that an exemplary electromagnetic signal is received byeach of ANTENNA ELEMENT A and ANTENNA ELEMENT B in quadrant I as anupright (positive) signal characteristic. Thus in FIG. 3, quadrant Iindicates that ANTENNA ELEMENT A receives a positive Gaussian doublet(indicated as A+) and ANTENNA ELEMENT B receives a positive Gaussiandoublet (indicated as B+).

Quadrant II lies on a different side of axis y than quadrant I; that isquadrant II is in a different half-plane of ANTENNA ELEMENT A thanquadrant I. It is for this reason that the Gaussian doublet of theelectromagnetic signal received (or transmitted) by ANTENNA ELEMENT A isinverted (negative) in quadrant II (indicated as A−). In contrast,quadrant II lies on the same side of axis x as quadrant I; that is,quadrant II is in the same half plane of ANTENNA ELEMENT B as quadrantI. It is for this reason that the Gaussian doublet of theelectromagnetic signal received (or transmitted) by ANTENNA ELEMENT B isupright (positive) in quadrant II (indicated as B+).

Quadrant III lies on a different side of axis y than quadrant I; that isquadrant II is in a different half-plane of ANTENNA ELEMENT A thanquadrant I. It is for this reason that the Gaussian doublet of theelectromagnetic signal received (or transmitted) by ANTENNA ELEMENT A isinverted (negative) in quadrant III (indicated as A−). Quadrant III lieson a different side of axis x as quadrant I; that is, quadrant III is ina different half plane of ANTENNA ELEMENT B as quadrant I. It is forthis reason that the Gaussian doublet of the electromagnetic signalreceived (or transmitted) by ANTENNA ELEMENT B is inverted (negative) inquadrant III (indicated as B−).

Quadrant IV lies on the same side of axis y as quadrant I; that isquadrant IV is in the same half-plane of ANTENNA ELEMENT A as quadrantI. It is for this reason that the Gaussian doublet of theelectromagnetic signal received (or transmitted) by ANTENNA ELEMENT A isupright (positive) in quadrant IV (indicated as A+). In contrast,quadrant IV lies on a different side of axis x as quadrant I; that is,quadrant IV is in a different half plane of ANTENNA ELEMENT B asquadrant I. It is for this reason that the Gaussian doublet of theelectromagnetic signal received (or transmitted) by ANTENNA ELEMENT B isinverted (negative) in quadrant IV (indicated as B−).

Thus, each respective sector or quadrant I, II, III, IV is uniquelyidentified by the characteristic Gaussian doublet of the received (ortransmitted) electromagnetic signal. Thus, ascertaining the combinationof states of Gaussian doublets of the received (or transmitted)electromagnetic signal by each of ANTENNA ELEMENTS A, B permitsascertaining angle of arrival of the electromagnetic signal at least toa resolution of one quadrant I, II, III, IV.

A radio transmission and reception system for use in conjunction withthe present invention may benefit from employing an original transmitbroadband signal with a reference: a predetermined signal characteristicor combination of signal characteristics employed as a reference signal.Such a reference may assist a receiver in distinguishing which of afirst or second state is indicated.

FIG. 4 is a schematic diagram illustrating patterns of waveforminversions related to sector of arrival of an electromagnetic signal ata multi-element antenna apparatus. In FIG. 4, antenna elements 12, 14are shown in a top view with their associated axes x₁, y₁, and antennaelements 32, 34 are shown in a top view with their associated axes x₂,y₂. Preferably plane x₁, y₁ is substantially coincident with plane x₂,y₂. A broadband electromagnetic signal containing a Gaussian doublet isreceived by antenna elements 12, 14, 32, 34. Antenna elements establishsectors I, II, III, IV, V, VI, VII, VIII. For purposes of succinctlydescribing operation of the apparatus illustrated in FIG. 4, antennaelement 12 will be referred to as ANTENNA ELEMENT A, antenna element 14will be referred to as ANTENNA ELEMENT B, antenna element 32 will bereferred to as ANTENNA ELEMENT C and antenna element 34 will be referredto as ANTENNA ELEMENT D.

FIG. 4 presumes that an exemplary electromagnetic signal is received byeach of ANTENNA ELEMENT A, ANTENNA ELEMENT B, ANTENNA ELEMENT C andANTENNA ELEMENT D in sector I as an upright (positive) signalcharacteristic. Gaussian doublets are indicated in FIG. 4 with anotation as to the respective antenna element receiving theelectromagnetic signal (i.e., ANTENNA ELEMENT A, B, C, or D) and anindication whether the respective Gaussian doublet is upright (i.e.,positive; +) or inverted (i.e., negative; −). Thus in FIG. 4, sector Iindicates that ANTENNA ELEMENT A receives a positive Gaussian doublet(indicated as A+), ANTENNA ELEMENT B receives a positive Gaussiandoublet (indicated as B+), ANTENNA ELEMENT C receives a positiveGaussian doublet (indicated as C+) and ANTENNA ELEMENT D receives apositive Gaussian doublet (indicated as D+).

Sector II lies on a different side of axis y₁ than sector I; that issector II is in a different half-plane of ANTENNA ELEMENT A than sectorI. It is for this reason that the Gaussian doublet of theelectromagnetic signal received (or transmitted) by ANTENNA ELEMENT A isinverted (negative) in sector II (indicated as A−). In contrast, sectorII lies on the same side of axis x₁ as sector I; sector II lies on thesame side of axis y₂ as sector I; and sector II lies on the same side ofaxis x₂ as sector I. That means that sector II is in the same half-planeof ANTENNA ELEMENT B as sector I, sector II is in the same half plane ofANTENNA ELEMENT C as sector I and sector II is in the same half plane ofANTENNA ELEMENT D as sector I. It is for this reason that the Gaussiandoublets of the electromagnetic signal received (or transmitted) byANTENNA ELEMENT B, ANTENNA ELEMENT C and ANTENNA ELEMENT D are upright(positive) in sector II (indicated as B+, C+, D+).

Sector III lies on a different side of axis y₁ than sector I, and sectorIII lies on a different side of axis y₂ than sector II. That is, sectorIII is in a different half-plane of ANTENNA ELEMENT A than sector I, andsector III is in a different half-plane of ANTENNA ELEMENT C than sectorII. It is for this reason that the Gaussian doublet of theelectromagnetic signal received (or transmitted) by ANTENNA ELEMENT A isinverted (negative) in sector III (indicated as A−) and the Gaussiandoublet of the electromagnetic signal received (or transmitted) byANTENNA ELEMENT C is inverted (negative) in sector III (indicated asC−). In contrast, sector III lies on the same side of axis x₁ as sectorsI and II, and sector III lies on the same side of axis x₂ as sectors Iand II. That means that sector III is in the same half-plane of ANTENNAELEMENT B as sectors I and II, and sector III is in the same half planeof ANTENNA ELEMENT D as sectors I and II. It is for this reason that theGaussian doublets of the electromagnetic signal received (ortransmitted) by ANTENNA ELEMENT B and ANTENNA ELEMENT D are upright(positive) in sector III (indicated as B+, C+).

Sector IV lies on a different side of axis y₁ than sector I; sector IVlies on a different side of axis x₁ than sectors I, II and III; andsector IV lies on a different side of axis y₂ than sectors I and II.That is, sector IV is in a different half-plane of ANTENNA ELEMENT Athan sector I; sector IV is in a different half-plane of ANTENNA ELEMENTB than sectors I, II and III; and sector IV is in a different half-planeof ANTENNA ELEMENT C than sectors I and II. It is for this reason thatthe Gaussian doublet of the electromagnetic signal received (ortransmitted) by ANTENNA ELEMENT A is inverted (negative) in sector IV(indicated as A−), the Gaussian doublet of the electromagnetic signalreceived (or transmitted) by ANTENNA ELEMENT B is inverted (negative) insector IV (indicated as B−) and the Gaussian doublet of theelectromagnetic signal received (or transmitted) by ANTENNA ELEMENT C isinverted (negative) in sector IV (indicated as C−). In contrast, sectorIV lies on the same side of axis x₂ as sectors I, II and III. That meansthat sector IV is in the same half-plane of ANTENNA ELEMENT D as sectorsI, II and III. It is for this reason that the Gaussian doublet of theelectromagnetic signal received (or transmitted) by ANTENNA ELEMENT D isupright (positive) in sector IV (indicated as D+).

Sector V lies on a different side of axis y₁ than sector I; sector Vlies on a different side of axis x₁ than sectors I, II and III; sector Vlies on a different side of axis y₂ than sectors I and II; and sector Vlies on a different side of axis x₂ than sectors I and II. That is,sector V is in a different half-plane of ANTENNA ELEMENT A than sectorI; sector V is in a different half-plane of ANTENNA ELEMENT B thansectors I, II and III; sector V is in a different half-plane of ANTENNAELEMENT C than sectors I and II; and sector V is in a differenthalf-plane of ANTENNA ELEMENT D than sectors I, II, III and IV. It isfor this reason that the Gaussian doublet of the electromagnetic signalreceived (or transmitted) by ANTENNA ELEMENT A is inverted (negative) insector V (indicated as A−), the Gaussian doublet of the electromagneticsignal received (or transmitted) by ANTENNA ELEMENT B is inverted(negative) in sector V (indicated as B−), the Gaussian doublet of theelectromagnetic signal received (or transmitted) by ANTENNA ELEMENT C isinverted (negative) in sector V (indicated as C−) and the Gaussiandoublet of the electromagnetic signal received (or transmitted) byANTENNA ELEMENT D is inverted (negative) in sector V (indicated as D−).Sector V does not lie in any same half-plane of any of ANTENNA ELEMENTA, ANTENNA ELEMENT B, ANTENNA ELEMENT C, ANTENNA ELEMENT D as sectors I.It is for this reason that none of the Gaussian doublets received (ortransmitted) by ANTENNA ELEMENT A, ANTENNA ELEMENT B, ANTENNA ELEMENT C,ANTENNA ELEMENT D is upright (positive) in sector V.

Sector VI lies on a different side of axis x₁ than sectors I, II andIII; sector VI lies on a different side of axis y₂ than sectors I andII; and sector VI lies on a different side of axis x₂ than sectors I,II, III and IV. That is, sector VI is in a different half-plane ofANTENNA ELEMENT B than sectors I, II and III; sector VI is in adifferent half-plane of ANTENNA ELEMENT C than sectors I and II; andsector VI is in a different half-plane of ANTENNA ELEMENT D than sectorsI, II, III and IV. It is for this reason that the Gaussian doublet ofthe electromagnetic signal received (or transmitted) by ANTENNA ELEMENTB is inverted (negative) in sector VI (indicated as B−), the Gaussiandoublet of the electromagnetic signal received (or transmitted) byANTENNA ELEMENT C is inverted (negative) in sector VI (indicated as C−)and the Gaussian doublet of the electromagnetic signal received (ortransmitted) by ANTENNA ELEMENT D is inverted (negative) in sector VI(indicated as D−). In contrast, sector VI lies on the same side of axisy₁ as sector I. That means that sector VI is in the same half-plane ofANTENNA ELEMENT A as sector I. It is for this reason that the Gaussiandoublet of the electromagnetic signal received (or transmitted) byANTENNA ELEMENT A is upright (positive) in sector VI (indicated as A+).

Sector VII lies on a different side of axis x₁ than sectors I, II andIII; and sector VII lies on a different side of axis x₂ than sectors I,II, III and IV. That is, sector VII is in a different half-plane ofANTENNA ELEMENT B than sectors I, II and III; and sector VII is in adifferent half-plane of ANTENNA ELEMENT D than sectors I, II, III andIV. It is for this reason that the Gaussian doublet of theelectromagnetic signal received (or transmitted) by ANTENNA ELEMENT B isinverted (negative) in sector VII (indicated as B−) and the Gaussiandoublet of the electromagnetic signal received (or transmitted) byANTENNA ELEMENT D is inverted (negative) in sector VII (indicated asD−). In contrast, sector VII lies on the same side of axis y₁ as sectorI, and sector VII lies on the same side of axis y₂ as sectors I and II.That means that sector VII is in the same half-plane of ANTENNA ELEMENTA as sector I, and sector VII is in the same half-plane of ANTENNAELEMENT C as sectors I and II. It is for this reason that the Gaussiandoublet of the electromagnetic signal received (or transmitted) byANTENNA ELEMENT A is upright (positive) in sector VII (indicated as A+)and the Gaussian doublet of the electromagnetic signal received (ortransmitted) by ANTENNA ELEMENT C is upright (positive) in sector VII(indicated as C+).

Sector VIII lies on a different side of axis x₂ than sectors I, II, IIIand IV. That is, sector VIII is in a different half-plane of ANTENNAELEMENT D than sectors I, II, III and IV. It is for this reason that theGaussian doublet of the electromagnetic signal received (or transmitted)by ANTENNA ELEMENT D is inverted (negative) in sector VIII (indicated asD−). In contrast, sector VIII lies on the same side of axis y₁ assectors I, VI, VII and VIII; sector VIII lies on the same side of axisx₁ as sectors I, II and III; and sector VIII lies on the same side ofaxis y₂ as sectors I, II and VII. That means that sector VIII is in thesame half-plane of ANTENNA ELEMENT A as sectors I, VI, VII and VIII;sector VIII is in the same half-plane of ANTENNA ELEMENT B as sectors I,II and III; and sector VIII is in the same half-plane of ANTENNA ELEMENTC as sectors I, II and VII. It is for this reason that the Gaussiandoublet of the electromagnetic signal received (or transmitted) byANTENNA ELEMENT A is upright (positive) in sector VIII (indicated asA+), the Gaussian doublet of the electromagnetic signal received (ortransmitted) by ANTENNA ELEMENT B is upright (positive) in sector VIII(indicated as B+) and the Gaussian doublet of the electromagnetic signalreceived (or transmitted) by ANTENNA ELEMENT C is upright (positive) insector VIII (indicated as C+).

Thus, each respective sector I, II, III, IV, V, VI, VII, VIII isuniquely identified by the characteristic Gaussian doublet of thereceived (or transmitted) electromagnetic signal. Thus, ascertaining thecombination of states of Gaussian doublets of the received (ortransmitted) electromagnetic signal by each of ANTENNA ELEMENTS A, B, C,D permits ascertaining angle of arrival of the electromagnetic signal atleast to a resolution of one quadrant I, II, III, IV, V, VI, VII, VIII.

FIG. 5 is a schematic diagram illustrating details of the preferredembodiment of an evaluation apparatus useful in the system of thepresent invention. In FIG. 5, a direction finding system 50 includes anantenna array 52 and an evaluation apparatus 54. Antenna array 52includes a first antenna element 56 and a second antenna element 58.Antenna elements 56, 58 are shown as planar loop antennas. A widevariety of other antennas are suitable for use in antenna array 52. Oneadvantage of planar loop antennas, however, is that such antennas may bemade arbitrarily small, limited only by a sensitivity of receiver units60, 62 in properly detecting signals from antenna elements 56, 58. Thus,an antenna array 52 may be made very compact.

Evaluation apparatus 54 includes a first receiver unit 60, a secondreceiver unit 62 and a processor unit 64. First receiver unit 60 iscoupled with one antenna element 56, 58 and second receiver unit 62 iscoupled with another antenna element 56, 58 than is coupled with firstantenna element 60. Each of receiver units 60, 62 provides informationrelating to signals received from its respective coupled antenna element56, 58 to processor unit 64. Preferably, receiver unit 60, 62 provideinformation relating to signal amplitude or strength (e.g., RSSI;Received Signal Strength Indication) and signal orientation (e.g.,Gaussian doublet upright [+] or inverted [−]) information.

Processing unit 64 employs predetermined relationships, preferablyalgorithmic relationships, for determining in which sector (FIG. 3) thesignal arrived (or was transmitted). Processor unit 64 may interpret thecombination of orientations of Gaussian doublets received by antennaelements 56, 58 to ascertain in which sector the signal arrived. In therepresentative situation illustrated in FIG. 5, first receiver unit 60receives a first signal from antenna element 56 that has an amplitude A₁and is an inverted Gaussian doublet. Second receiver unit 62 receives asecond signal from antenna element 58 that has an amplitude A₂ and is anupright Gaussian doublet. By such determinations, processor unit 64 mayascertain angle of arrival of a signal at direction finding system 50 toa resolution of one sector (FIG. 3). Further, by comparing signalamplitudes of arriving signals, processor unit 64 may ascertain whicharriving signals are directly received from a distal transmitter andwhich signals are received along a multi-path route having reflected offof an obstacle such as a building or other structure en route from thedistal transmitter to direction finding system 50. Processor unit 64presents an output signal at an output locus 66 to indicate conclusionsregarding signals arriving at antenna elements 56, 58.

FIG. 6 is a schematic diagram illustrating details of a first alternateembodiment of an evaluation apparatus useful in the system of thepresent invention. In FIG. 6, a location aware radio receiver system 150includes an antenna array 152 and an evaluation apparatus 154. Antennaarray 152 includes a first antenna element 156 and a second antennaelement 158.

Evaluation apparatus 154 includes a first receiver unit 160, a secondreceiver unit 162 and a processor unit 164. First receiver unit 160 iscoupled with one of antenna elements 156, 158 and second receiver unit162 is coupled with another of antenna elements 156, 158. Each ofreceiver units 160, 162 provides information relating to signalsreceived from its respective coupled antenna element 156, 158 toprocessor unit 164. Preferably, receiver units 160, 162 provideinformation relating to signal amplitude or strength (e.g., RSSI;Received Signal Strength Indication) and signal orientation (e.g.,Gaussian doublet upright [+] or inverted [−]) information.

Processing unit 64 includes a signal combiner unit 163 coupled with aprocessor 165. Signal combiner unit 163 combines signals received fromreceiver units 160, 162 according to assigned weight factors andpolarity factors. Weight factors and polarity factors are determinedaccording to predetermined relationships, such as algorithmicrelationships, using information conveyed by receiver units 160, 162relating to then extant signals received by antenna elements 156, 158. Asignal relating the combined signal information is conveyed to processor165, as indicated by arrow 167. Processor 165 evaluates informationprovided by signals received from combiner unit 163 and provides controlsignals, as indicated by arrow 169, to combiner unit 163 to adjustfactors such as weights applied to signals received from receiver units160, 162. It is by such adjustment of weight factors, for example, thatpermits location aware radio receiver system 150 to be electronicallysteered to concentrate upon selected signals. Evaluation of features ofreceived signals, such as amplitude or timing (when a means is providedfor determining timing) permit processor 165, for example, to ascertainwhich signals are directly received from a distal transmitter and whichsignals are received along a multi-path route having reflected off of anobstacle such as a building or other structure en route from the distaltransmitter to location aware radio receiver system 150. Determiningtiming may be effected, by way of example and not by way of limitation,by feedback from location aware radio receiver system 150 to atransmitter reporting time of arrival of an identifiable signal, or byreceipt of a timing signal with received signals or by anotherindependent time-determining arrangement. Processor 165 employspredetermined relationships, preferably algorithmic relationships, fordetermining in which sector (FIG. 3) the signal arrived (or wastransmitted). Processor 165 may interpret the combination oforientations of Gaussian doublets received by antenna elements 156, 158to ascertain in which sector the signal arrived. By such determinations,processor 165 may ascertain angle of arrival of a signal at locationaware radio receiver system 150 to a resolution of one sector (FIG. 3).Further, by electronically steering location aware radio receiver system150 as described above by adjusting weights assigned to receivedsignals, location aware radio receiver system 150 may ignore multi-pathsignals and concentrate reception toward direct signals. Processor unit164 presents an output signal at an output locus 166 to indicateconclusions regarding signals arriving at antenna elements 156, 158.

FIG. 7 is a schematic diagram illustrating details of a second alternateembodiment of an evaluation apparatus useful in the system of thepresent invention. In FIG. 7, a direction finding system 250 includes anantenna array 252 and an evaluation apparatus 254. Antenna array 252includes a first antenna element 256 and a second antenna element 258.

Evaluation apparatus 254 includes a receiver unit 260 and a processorunit 264. Receiver unit 260 includes a signal delay unit 262, a signalcombining unit 265 and a receiver 267. Signal delay unit 262 is coupledwith antenna element 256 and with combining unit 265. Combining unit 265is also coupled with antenna element 258. Signal delay unit 265 imposesa delay on signals received from antenna element 256 and provides thosedelayed signals to combining unit 265. Combining unit 265 combinesdelayed signals received from signal delay unit 265 and real-time ornon-delayed signals received from antenna element 258 to present asignal stream to receiver 267. In the exemplary embodiment of theinvention illustrated in FIG. 7, receiver 267 receives a signal streamincluding a first signal from antenna element 258 that has an amplitudeA₁ and is a noninverted (U, or +) Gaussian doublet and including asecond signal (received from antenna element 256) that is delayed intime with respect to the signal received by antenna element 258. Thesecond delayed signal has an amplitude A₂ and is an inverted (I or −)Gaussian doublet. Receiver 267 provides the signal stream containingreal-time and delayed signals to processor unit 264. Preferably,receiver 267 provides information relating to signal amplitude orstrength (e.g., RSSI; Received Signal Strength Indication) and signalorientation (e.g., Gaussian doublet upright [+] or inverted [−])information to processor unit 264.

Processor unit 64 employs predetermined relationships, preferablyalgorithmic relationships, for determining in which sector (FIG. 3) thesignal arrived (or was transmitted). Processor unit 264 may interpretthe combination of orientations of Gaussian doublets received by antennaelements 256, 258 to ascertain in which sector the signal arrived. Bysuch determinations, processor unit 264 may ascertain angle of arrivalof a signal at direction finding system 250 to a resolution of onesector (FIG. 3). Further, by comparing signal amplitudes of arrivingsignals, processor unit 264 may ascertain which arriving signals aredirectly received from a distal transmitter and which signals arereceived along a multi-path route having reflected off of an obstaclesuch as a building or other structure en route from the distaltransmitter to direction finding system 250. Processor unit 264 presentsan output signal at an output locus 266 to indicate conclusionsregarding signals arriving at antenna elements 256, 258.

FIG. 8 illustrates a planar antenna for use with the present invention.In FIG. 8, an antenna 800 presents a two lobe or “quadrupole” typepattern in which each lobe 802, 804 has a field sense opposite to theother. Antenna 800 has a differential feed 810 that is formed by a slot812 between a minus (−) element 814 in lobe 802 and a plus (+) element816 in lobe 804. Differential feed 810 terminates at a neutral element820 in a feed region 822. The combination of minus (−) element 814, plus(+) element 816 and neutral element 820 at feed region 822 acts so assplit a signal with a polarity denoted by arrow 824 into two signals ofopposing polarity: a first signal 830 of polarity α that becomes aradiated signal 832 of polarity β and a second signal 834 of polarity δthat becomes a radiated signal 836 of polarity ε. For ease ofexplanation, the behavior of a planar antenna of FIG. 8 is explained interms of radiation with lobe 802 having polarity β and lobe 804 havingpolarity δ. Antenna 800 may also be used for reception.

FIG. 9 illustrates a representative signal pattern of the antenna ofFIG. 8. In FIG. 9, a signal pattern 900 is established by antenna 800.Signal pattern 900 is a two lobe or “quadrupole” type pattern in whicheach lobe 802, 804 has a field sense or polarity β, ε opposite to theother. Because this pattern is insensitive in directions notsubstantially lying on an azimuthal plane, the pattern is characterizedby a higher gain than the dipole doughnut pattern of a loop antenna.

FIG. 10 illustrates a novel chiral polarization UWB slot antenna. InFIG. 10, a chiral polarization ultra-wide band (“UWB”) slot antenna 1000is suitable for many applications, including for use in conjunction withthe present invention. Chiral polarization UWB slot antenna 1000 can bemade in a smaller structure than a single polarization UWB antenna.Antenna 1000 is preferably approximately λ/π in its greatest dimension.This dimension is approximately 36% smaller than a typical λ/2 UWBdipole where λ is the wavelength at a typical center frequency of theantenna. The chiral polarization slot UWB design of antenna 1000includes opposing tapered slot lines 1002, 1004 each in an approximately180° arc with an arc length substantially equal to λ/2 at a particularcenter frequency of interest. Each slot line terminates in a bulbous end1006, 1008 which approximates an electrical open or free space impedanceat frequencies of interest. It should be understood that discussions ofimpedance refer to a characteristic impedance in a particular frequencyband of interest. Thus, although bulbous ends 1006, 1008 are electricalshorts at DC or low frequencies, bulbous ends 1006, 1008 can be designedto match a desired open or free space impedance within a frequency bandof interest. Tapered slot lines 1002, 1004 and bulbous ends 1006, 1008are shown in FIG. 10 as voids in a metal layer 1009. Metal layer 1009may optionally be attached to a dielectric substrate (not shown).

Antenna 1000 will exhibit quadrupole pattern lobes normal to metal layer1009. Antenna 1000 is sensitive to chiral polarized signals of differentorientations on opposite sides. On one side, antenna 1000 will besensitive to right-hand chiral (RHC) signals, while on an opposing side,antenna 1000 will be sensitive to left-hand chiral (LHC) signals. Thus(by way of example), an array 52 involving two pairs of antenna 1000would suffice to provide sensitivity to either LHC or RHC along eitherof two orthogonal coordinate axes. Such a four element array 52 (notshown in FIG. 10) might be used in an embodiment of the presentinvention in which polarization is employed as a signal characteristic.

FIG. 11 illustrates a dual horn antenna system for use with the presentinvention. In FIG. 11, a dual horn antenna system 1100 is constructedwith a top metallization pattern establishing a first dual horn antenna1102 on a planar substrate 1103 and a bottom metallization patternestablishing a second dual horn antenna 1104 on substrate 1103. Eachdual horn antenna 1102, 1104 exhibits a dual-lobed or quadrupole typeantenna pattern. Each dual horn antenna 1102, 1104 is oriented at 90degrees relative to the other dual horn antenna 1102, 1104. Radiationfrom each dual horn antenna 1102, 1104 system is polarized in the planeof substrate 1103.

FIG. 12 provides an isometric view of the dual horn antenna system ofFIG. 11. In FIG. 12, arrows 1202, 1204 denote the directions of patternlobes for dual horn antennas 1102, 1104.

FIG. 13 illustrates shows a transmitter and a receiver employedaccording to the teachings of the present invention. In FIG. 13, atransmitter 1300 radiates a transmitted waveform at a time t₀ to areceiver 1302. By way of illustration and not by way of limitation,transmitter 1300 and receiver 1302 are in the vicinity of a reflectingobject 1304 thus creating a multi-path propagation environment in whichreceiver 1302 captures radio wave signals from a first signal path(1321), a second signal path (1322), a third signal path (1323), and afourth signal path (1324) with angles of incidence θ₁, θ₂, θ₃, θ₄.Signals traversing signal paths 1321, 1322, 1323, 1324 arrive at timest₁, t₂, t₃, t₄ after following paths of length L₁ (signal path 1321), L₂(signal path 1322), L₃ (signal path 1323), L₄ (signal path 1324).Arrival times t₁, t₂, t₃, t₄ vary linearly with path lengths L₁, L₂, L₃,L₄, and complete signal paths 1321, 1322, 1323, 1324 at the speed oflight c. Thus a measurement of arrival times t₁, t₂, t₃, t₄ alsoeffectively measures path lengths L₁, L₂, L₃, L₄. Signal path 1321 is adirect, line-of-sight path. Signal paths 1322, 1323, 1324 are indirectpropagation paths that involve a reflection or bounce. For example,signal path 1324 begins at transmitter 1300, continues to a point ofreflection 1330, and further continues on to receiver 1302. For purposeof illustration, reflecting object 1304 is a single object such as awall. A typical propagation environment may be defined by a complicatedcombination of multiple reflecting objects such as reflecting object1304. FIG. 14 illustrates a typical transmitted signal and receivedsignals in a multi-path environment such as may be received by anantenna system as taught by the present invention. In FIG. 14, atransmit signal is illustrated, and several received signals areillustrated representing how the transmit signal appears inrepresentative antennas: a signal #0 received in an omni-directionalsense antenna, Signal #1 with amplitude A₁ received in a firstdirectional antenna sensitive in the ±x-direction and Signal #2 withamplitude A₂ received in a second antenna sensitive in the ±y-direction.These amplitudes A₁, A₂ are preferentially obtained from a direct,line-of-sight path such as a first signal path 1321 (FIG. 13). For easeof illustration, the transmit signal is depicted as a simple monocyclewaveform, but any other waveform, pulse shape, or waveform packet may beused in conjunction with the present invention. Received signals such asSignal #0, Signal #1, and Signal #2 are composed of a variety ofwavelets: a first wavelet due to a signal arriving from a first path, asecond wavelet arriving from a second path, a third wavelet arrivingfrom a third path, and a fourth wavelet arriving from a fourth path. Asreceived by an omni-directional antenna in Signal #0, a first wavelet isdue to a line-of-sight direct signal path and has an orientationsubstantially similar to the transmitted waveform. A second wavelet, athird wavelet, and a fourth wavelet are due to a second path, a thirdpath, and a fourth path (respectively) that involve a single reflection.Thus, a second wavelet, a third wavelet, and a fourth wavelet areinverted relative to a first wavelet in Signal #0. Signal #1 and Signal#2 are composed of wavelets that may or may not be inverted depending onthe combination of one or more inversions due to propagation path andinversions due to the behavior of the angle of arrival antenna system.For ease of illustration, a transmitted signal has been depicted onlyslightly larger than Signal #0, Signal #1, and Signal #2. Typically atransmit signal is much larger than a received signal.

Also for ease of illustration, Signal #1 and Signal #2 are scaledrelative to Signal #0 under the assumption that the gain of a firstdirectional antenna and a second directional antenna is substantiallyequivalent to the gain of an omni-directional sense antenna. In general,however, a first directional antenna and a second directional antennawill have a gain greater than an omni-directional sense antenna, and soSignal #1 and Signal #2 will have a greater amplitude (relative toSignal #0) than depicted.

The angle of arrival, subject to an ambiguity of quadrant (θ′), may befound from amplitude comparison: $\begin{matrix}{\theta^{\quad\prime} = {\arctan\frac{A_{2}}{A_{1}}}} & \lbrack 4\rbrack\end{matrix}$

Following the teachings of the present invention, the quadrant ofarrival may be determined unambiguously by a comparison of signalpolarity, thus allowing for an unambiguous determination of angle ofincidence, θ₁.

Note that Signal #0 from an omni-directional sense antenna is notrequired to determine an angle of incidence θ₁ if amplitudes A₁, A₂ areobtained from a first wavelet due to a direct, line-of-sight path (e.g.,signal path 1321; FIG. 13). This angle of incidence from a direct,line-of-sight path θ₁ (FIG. 13) is also an angular relationship θ₁ of atransmitter relative to a receiver. An angular relationship θ₁ inconjunction with a path length L₁, defines the position of a transmitterrelative to a receiver. Thus, the present invention enablesdetermination of the position of a transmitter without reliance on amulti-lateration calculation based on path lengths obtained from anetwork of path length measurements. Alternatively or in addition, theangle of arrival measurements possible using the present invention maybe used to refine or improve a multi-lateration calculation based onpath lengths obtained from a network of path length measurements.

If amplitudes A₁, A₂ are obtained from a second wavelet, a thirdwavelet, or a fourth wavelet, due to a second path (1322), a third path(1323), or a fourth path (1324) that are indirect propagation paths thatinvolve a reflection or bounce, then a Signal#0 from an omni-directionalsense antenna is useful. A Signal #0 exhibits the inversions due to thepropagation path, allowing them to be distinguished from the inversionsdue to the function of the angle of arrival antenna system.

Thus, an angle-of-arrival antenna system does not require anomni-directional sense antenna but may benefit from one in the presenceof significant multi-path signals.

Typically, a first directional antenna and a second directional antennahave higher gain than an omni-directional signal, so one or both ofamplitudes A₁, A₂ will be larger than amplitude A₀. Thus a signalobtained from a combination of Signal #1 and Signal #2 is typicallygreater in amplitude than A₀.

A typical rake receiver takes a signal such as Signal#0 and detects andcombines energy arriving at times t₁, t₂, t₃, t₄ so as to maximize areceived signal to noise. The present invention enables a “spatial-rakereceiver,” one in which signals such as Signal#1 (S1) and Signal#2 (S2)are combined not only in time but also in space so as to create areceived signal (S). If useful wavelets are found arriving at times t₁,t₂, t₃, t₄, a spatial rake might combine these signals as follows:S=K ₁₁ S 1|_(t) ₁ _(±Δt) +K ₁₂ S 2|_(t) ₁ _(±Δt)+K₂₁ S 1|_(t) ₂ _(±Δ) +K ₂₂ S 2|_(t) ₂ _(±Δt)+K₃₁ S 1|_(t) ₃ _(±Δt) +K ₃₂ S 2|_(t) ₃ _(±Δt)+K₄₁ S 1|_(t) ₄ _(±Δt) +K ₄₂ S 2|_(t) ₄ _(±Δt)  [5]

where S1|_(t) ₁ _(±Δt) is Signal #1 evaluated at times within Δt of t₁so as to capture energy in a first wavelet, S2|_(t) ₃ _(±Δt) is Signal#2 evaluated at times within Δt of t₂ so as to capture energy in asecond wavelet, and so on.

An exemplary spatial rake receiver might (for instance) construct areceived signal (S) using angle of arrival information usingcoefficients:

 K ₁₁=cos θ₁ , K ₂₁=cos θ₂ , K ₃₁=cos θ₃ , K ₄₁=cos θ₄  [6]K ₁₂=sin θ₁ , K ₂₂=sin θ₂ , K ₃₂=sin θ₃ , K ₄₂=sin θ₄  [7]

In effect, these coefficients are equivalent to a rotation of a virtualantenna pattern oriented according to a choice of angle—thus making areceiver more or less sensitive in particular directions. In generalhowever, a spatial rake receiver would use angle of arrival informationas a starting point and vary the coefficients depending on theidiosyncrasies of the noise and interference environment so as tomaximize the signal to noise ratio of received signal S. Additionally, aspatial rake receiver might act so as to minimize the impact of aninterfering signal arriving from a particular direction by orienting anull of a virtual pattern so as to minimize sensitivity of a receiver tosignals arriving from a direction in which there is undesiredinterference. Note that a spatial rake receiver as envisioned by thepresent invention does not require an omni-directional sense antenna.

If an indirect propagation path involves a single reflection or bouncesuch as a fourth signal path 1324 (FIG. 13), then a point of reflectionmust lie on an elliptical arc defined by foci at transmitter 1300 andreceiver 1302and by the path length L₄. If an angle of incidence θ₄ isknown, then the position of a point of reflection may be unambiguouslyidentified. Thus, an angle of arrival system as taught by the presentinvention can identify the specific location of a point of reflection.

In a static environment the present invention may be used in conjunctionwith a radar intrusion detection system, allowing such a system toidentify the specific location of an intruder. An object moving withinthe propagation environment between a transmitter and a receiver may betracked using an angle of arrival system as taught by the presentinvention. Al so, the location of walls or other static reflectingobjects in the propagation environment may be determined.

In a dynamic environment with either a moving transmitter, a movingreceiver, or both, a transmitter and a receiver with an angle of arrivalsystem as taught by the present invention can compile data regarding thelocation of a point of reflection and create a radar map of thesurrounding environment.

The present discussion has focused on use of an angle of arrival antennasystem acting as a receiver. This does not preclude applying theteachings of the present invention in conjunction with transmission. Bythe principle of reciprocity for instance, an antenna system of the kindtaught by the present invention can transmit a time-reversed signal withrelatively dispersed energy with respect to time and result in aconcentrated energy or impulsive signal at a receiver. Similarly, justas the present invention can reduce sensitivity of a receiver tointerference by orienting a null of a virtual antenna pattern in aparticular direction, so also can the present invention reducetransmitted power in a particular direction to avoid interference with afriendly receiver known to lie in that direction.

FIG. 15 is a flow chart illustrating the method of the presentinvention. In FIG. 15, a method 1500 for ascertaining angle of arrivalof an electromagnetic signal at an antenna structure begins at a STARTlocus 1502. Method 1500 continues with the step of, in no particularorder (1) configuring the antenna structure to include a plurality of nantenna elements intersecting a common axis and cooperating to establish2n sectors; each respective sector of the 2n sectors being defined bytwo the antenna elements of the plurality of n antenna elements and theaxis, as indicated by a block 1504; and (2) providing theelectromagnetic signal with at least one signal characteristic; the atleast one signal characteristic indicating a first state on a first sideof each respective antenna element of the n antenna elements andindicating the second state on a second side of each the respectiveantenna element of the plurality of n antenna elements; combinations ofthe signal characteristics in each the respective sector uniquelyidentifying the respective sector, as indicated by a block 1506.

Method 1500 continues with the step of evaluating the state of thesignal characteristic sensed by each the respective antenna element toeffect the ascertaining angle of arrival to a resolution of at least onethe respective sector, as indicated by a block 1508. Method 1500terminates ant an END locus 1510.

It is to be understood that, while the detailed drawings and specificexamples given describe preferred embodiments of the invention, they arefor the purpose of illustration only, that the apparatus and method ofthe invention are not limited to the precise details and conditionsdisclosed and that various changes may be made therein without departingfrom the spirit of the invention which is defined by the followingclaims:

1. A system for ascertaining angle of arrival of an electromagneticsignal; said electromagnetic signal having at least one signalcharacteristic; said at least one signal characteristic indicating afirst state or a second state; the system comprising: (a) a plurality ofn antenna elements intersecting a common axis and cooperating toestablish 2n sectors; each respective sector of said 2n sectors beingdefined by two said antenna elements of said plurality of n antennaelements and said axis; said signal characteristic indicating said firststate on a first side of each respective antenna element of said nantenna elements and indicating said second state on a second side ofeach said respective antenna element; combinations of said signalcharacteristics in each said respective sector uniquely identifying saidrespective sector; and (b) an evaluation apparatus coupled with at leasttwo antenna elements of said plurality of n antenna elements; saidevaluation apparatus employing said state of said signal characteristicsensed by each of said at least two antenna elements to effect saidascertaining angle of arrival to a resolution of at least one saidrespective sector.
 2. A system for ascertaining angle of arrival of anelectromagnetic signal as recited in claim 1 wherein said each antennaelement of said plurality of n antenna elements is substantially planar.3. A system for ascertaining angle of arrival of an electromagneticsignal as recited in claim 1 wherein said at least one signalcharacteristic indicates said first state and said second state in atime domain.
 4. A system for ascertaining angle of arrival of anelectromagnetic signal as recited in claim 2 wherein said at least onesignal characteristic indicates said first state and said second statein a time domain.
 5. A system for ascertaining angle of arrival of anelectromagnetic signal as recited in claim 1 wherein said evaluationapparatus comprises a respective receiver unit for each respective saidantenna element and at least one processing unit; said at least oneprocessor unit being coupled with each said respective receiver unit;each said receiver unit providing signal amplitude information andinformation relating to said at least one signal characteristic statefor a respective antenna element to said at least one processing unit;said at least one processing unit employing predetermined relationshipsand said information relating to said at least one signal characteristicstate for each at least two said respective antenna elements foreffecting said ascertaining angle of arrival.
 6. A system forascertaining angle of arrival of an electromagnetic signal as recited inclaim 2 wherein said evaluation apparatus comprises a respectivereceiver unit for each respective said antenna element and at least oneprocessing unit; said at least one processor unit being coupled witheach said respective receiver unit; each said receiver unit providingsignal amplitude information and information relating to said at leastone signal characteristic state for a respective antenna element to saidat least one processing unit; said at least one processing unitemploying predetermined relationships and said information relating tosaid at least one signal characteristic state for each at least two saidrespective antenna elements for effecting said ascertaining angle ofarrival.
 7. A system for ascertaining angle of arrival of anelectromagnetic signal as recited in claim 1 wherein said evaluationapparatus comprises a respective receiver unit for each respective saidantenna element and at least one processing unit; said at least oneprocessor unit being coupled with each said respective receiver unit;each said receiver unit providing signal amplitude information andinformation relating to said at least one signal characteristic statefor a respective antenna element to said at least one processing unit;said processing unit employing first predetermined relationships andsaid information relating to said at least one signal characteristicstate for assigning weighting to information received from each saidantenna element for effecting said ascertaining angle of arrival; saidprocessing unit further employing second predetermined relationships andsaid at least one signal characteristic state for adjusting saidweighting assigning to orient a virtual antenna pattern for saidplurality of n antenna elements.
 8. A system for ascertaining angle ofarrival of an electromagnetic signal as recited in claim 2 wherein saidevaluation apparatus comprises a respective receiver unit for eachrespective said antenna element and at least one processing unit; saidat least one processor unit being coupled with each said respectivereceiver unit; each said receiver unit providing signal amplitudeinformation and information relating to said at least one signalcharacteristic state for a respective antenna element to said at leastone processing unit; said processing unit employing first predeterminedrelationships and said information relating to said at least one signalcharacteristic state for assigning weighting to information receivedfrom each said antenna element for effecting said ascertaining angle ofarrival; said processing unit further employing second predeterminedrelationships and said at least one signal characteristic state foradjusting said weighting assigning to orient a virtual antenna patternfor said plurality of n antenna elements.
 9. A system for ascertainingangle of arrival of an electromagnetic signal as recited in claim 1wherein said evaluation apparatus comprises a signal delay unit, asignal combining unit, a single receiver unit and a processing unit;said signal delay unit and said signal combining unit being coupled withsaid plurality of n antenna elements; said signal delay unit imposing atleast one predetermined delay to selected signals received by saidplurality of n antenna elements; said signal combining unit receivingsignals from said plurality of n antenna elements and receiving delayedsignals from said signal delay unit; said signal combining unitcombining said received signals and said delayed signals into a signalstream; said receiver unit receiving said signal stream and providingsaid signal stream to said at least one processing unit; said at leastone processing unit employing predetermined relationships and saidinformation relating to said at least one signal characteristic state ofsaid received signal and said delayed signals for effecting saidascertaining angle of arrival.
 10. A system for ascertaining angle ofarrival of an electromagnetic signal as recited in claim 4 wherein n isfour.
 11. A system for ascertaining angle of arrival of anelectromagnetic signal as recited in claim 4 wherein n is two.
 12. Asystem for ascertaining angle of arrival of an electromagnetic signal;said electromagnetic signal having a signal characteristic indicating afirst state or a second state; the system comprising: (a) a plurality ofantenna elements intersecting a common axis and cooperating to establisha plurality of sectors; each respective sector of said plurality ofsectors being defined by two respective adjacent antenna elements ofsaid plurality of antenna elements and said axis; said signalcharacteristic indicating said first state on a first side of eachrespective antenna element of said plurality of antenna elements andindicating said second state on a second side of each said respectiveantenna element; combinations of said signal characteristics in eachsaid respective sector uniquely identifying said respective sector; and(b) an evaluation apparatus coupled with said plurality of antennaelements; said evaluation apparatus employing said state of said signalcharacteristic sensed by each of said respective antenna elements toeffect said ascertaining angle of arrival to a resolution of at leastone said respective sector.
 13. A system for ascertaining angle ofarrival of an electromagnetic signal as recited in claim 12 wherein saideach said respective antenna element is substantially planar.
 14. Asystem for ascertaining angle of arrival of an electromagnetic signal asrecited in claim 12 wherein said signal characteristic indicates saidfirst state and said second state in a time domain.
 15. A system forascertaining angle of arrival of an electromagnetic signal as recited inclaim 13 wherein said signal characteristic indicates said first stateand said second state in a time domain.
 16. A system for ascertainingangle of arrival of an electromagnetic signal as recited in claim 12wherein said evaluation apparatus comprises a respective receiver unitfor each respective said antenna element and at least one processingunit; said at least one processor unit being coupled with each saidrespective receiver unit; each said receiver unit providing signalamplitude information and information relating to said at least onesignal characteristic state for a respective antenna element to said atleast one processing unit; said at least one processing unit employingpredetermined relationships and said information relating to said atleast one signal characteristic state for each at least two saidrespective antenna elements for effecting said ascertaining angle ofarrival.
 17. A system for ascertaining angle of arrival of anelectromagnetic signal as recited in claim 13 wherein said evaluationapparatus comprises a respective receiver unit for each respective saidantenna element and at least one processing unit; said at least oneprocessor unit being coupled with each said respective receiver unit;each said receiver unit providing signal amplitude information andinformation relating to said at least one signal characteristic statefor a respective antenna element to said at least one processing unit;said at least one processing unit employing predetermined relationshipsand said information relating to said at least one signal characteristicstate for each at least two said respective antenna elements foreffecting said ascertaining angle of arrival.
 18. A system forascertaining angle of arrival of an electromagnetic signal as recited inclaim 12 wherein said evaluation apparatus comprises a respectivereceiver unit for each respective said antenna element and at least oneprocessing unit; said at least one processor unit being coupled witheach said respective receiver unit; each said receiver unit providingsignal amplitude information and information relating to said signalcharacteristic state for a respective antenna element to said at leastone processing unit; said processing unit employing first predeterminedrelationships and said information relating to said signalcharacteristic state for assigning weighting to information receivedfrom each said antenna element for effecting said ascertaining angle ofarrival; said processing unit further employing second predeterminedrelationships and said at least one signal characteristic state foradjusting said weighting assigning to orient a virtual antenna patternfor said plurality of n antenna elements.
 19. A system for ascertainingangle of arrival of an electromagnetic signal as recited in claim 13wherein said evaluation apparatus comprises a respective receiver unitfor each respective said antenna element and at least one processingunit; said at least one processor unit being coupled with each saidrespective receiver unit; each said receiver unit providing signalamplitude information and information relating to said signalcharacteristic state for a respective antenna element to said at leastone processing unit; said processing unit employing first predeterminedrelationships and said information relating to said signalcharacteristic state for assigning weighting to information receivedfrom each said antenna element for effecting said ascertaining angle ofarrival; said processing unit further employing second predeterminedrelationships and said at least one signal characteristic state foradjusting said weighting assigning to orient a virtual antenna patternfor said plurality of n antenna elements.
 20. A method for ascertainingangle of arrival of an electromagnetic signal at an antenna structure;the method comprising the steps of: (a) in no particular order: (1)configuring said antenna structure to include a plurality of n antennaelements intersecting a common axis and cooperating to establish 2nsectors; each respective sector of said 2n sectors being defined by twosaid antenna elements of said plurality of n antenna elements and saidaxis; and (2) providing said electromagnetic signal with at least onesignal characteristic; said at least one signal characteristicindicating a first state on a first side of each respective antennaelement of said n antenna elements and indicating said second state on asecond side of each said respective antenna element of said plurality ofn antenna elements; combinations of said signal characteristics in eachsaid respective sector uniquely identifying said respective sector; and(b) evaluating said state of said signal characteristic sensed by eachsaid respective antenna element to effect said ascertaining angle ofarrival to a resolution of at least one said respective sector.